Installing New Sear Housing Block - Walther P99

I've got an Interarms P99 made in 98, I've had it since 01. The ejector broke, which is part of the sear hosuing assembly. I called S&W and they said I could replace the whole sear housing assembly which was about $75 or just get the block, which was about $7 and transfer everything over......I opted for the $7 solution since I've been through the armorers class for the P99/SW99....although it was 5 years ago.....and also have been through the ones for Colt, SIG, and Glock, so I have some expirence. They were nice enough to send me the new sear housing block at no charge. I removed the old block, and switched everything over to the new block.....but my manual from armorers class only sorta kinda shows how the single action sear is installed (It does say emphatically it shouldn't be disassembled but I didn't have a lot of choice)....and I must not have done it right because after reassembly the pistol works in double action mode only but not single action......so I must not have the interaction of the single action sear and the single action lever....and am looking for knowledge. I know this is a pretty esoteric question but nothing venturered nothing gained.